AbstractBecause gliders are heavier than air, they can only fly aerodynamically. The high energy potential of the air pressure disenchanted the phenomenon fly because even the smallest differences in pressure cause high forces. The effects of Bernoulli does not disclose the basic principle of flying because the airflow according to Bernoullis experimental setup does not exist in this manner while flying. There is no relevant airflow, the aircraft is in motion, the air is nearly calm. The energy is in the airplane (potential energy) and not in the air. Gliders slide on an inclined path, so they losing potential energy permanently. Air can push with pressure only, it can not "pull" so that negative or less pressure only causes pressure differences and thus the relatively higher pressure can act. In order to counteract the gravity the sum of all pressure forces which acting on the plane, especially on the wing, must directed upwards, this means directed against the gravity. To make it easier to illustrate: a pressure difference of z. B. 1/333 bar on the wing is sufficient to keep the aircraft in the air.
In the movement the bottomside of the wing profile catches air and push it downward, while they are more or less evenly accelarated downwards (actio / reactio) a counterforce arises. By inertia additionally a slight overpressure is formed. On the top surface a space opens in the movement of the wing by the falling profile contour. By the inertia (toughness) this cannot be filled up immediately completly with air, a area of relatively low pressure is created. As a result, the air mass is deflected down both from the bottom and from the top surface. This mass offset acts opposite to the wing back (actio reactio). In the motion, these positive and negative pressure areas are permanently newly formed and exist in the area of the airfoil. There is left a downwash of air behind the wing that dissolves slowly on the wingtips. This downwash mix with the stationary ambient air in the form of vortices.
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what happens at the airfoil ⇐ |